This invention relates to ignition systems for internal combustion engines and, more particularly, to all electronic, compensating, and high energy improvements of the same.
Conventional vehicular ignition systems, such as, for example, of the Kettering type, generate high voltage sparks suitable for firing the engine's combustion chambers at predetermined engine angular positions. Such ignition systems of the inductive storage type commonly comprise a pair of mechanical breaker points series connected to the primary of an autoformer, otherwise known as the ignition coil. The breaker points are closed for a predetermined period, commonly referred to as dwell time, whereby energy is built up in the primary of the coil. At a predetermined engine angular position the points open, which, via the turns ratio of the coil, produces a high voltage spark at the coil secondary output.
A fundamental problem with such inductive storage type systems is that spark energy decreases with increasing engine RPM. The breaker points open and close at a constant percent duty cycle rate, thereby effecting a constant dwell angle ignition control. With increasing engine RPM the period of the engine cycle decreases whereby the time required to traverse the constant dwell angle decreases. The resultant shorter dwell times leads to an increased probability of engine misfiring.
The advent of fully electronic ignition systems has resulted in considerable improvements over conventional breaker point ignitions. Specifically, the short lived and unreliable breaker points have been replaced with optical or reluctance type sensors which seldom require maintenance. Further, the electronic systems allow the circuit designer to electrically control the dwell period. Thus, a family of "high energy" electronic ignition systems has evolved. Nonetheless, significant problems with such systems still arise. For example, many electronic ignitions which employ reluctance type pickups sense engine RPM by the amplitude of the induced sensor signal. While the sensor signal amplitude is a fuction of engine RPM, it is also a function of variables such as the gap between the sensor and rotating sensing element, as well as the inductance of the sensor pickup coil. Undesired changes in either of the above variables necessarily leads to an error in the resultant ignition system, whereby frequent maintenance is required to avoid engine misfiring. Also, electronic systems which maintain longer dwell times can lead to wasted heat energy in the coil. During dwell time the current through the coil increases exponentially, whereby for long dwell times a considerable current is established. Since the coil has an intrinsic internal resistance a resultant I.sup.2 R power is generated.
Finally, a fundamental problem with all conventional ignition systems is that they are subject to environmental effects as well as aging. Fluctuations in the battery voltage, as with temperature, may significantly affect the available spark energy from the ignition.